Thursday, January 6, 2011


The Virtual Retinal Display (VRD) is a personal display device under development at the University of Washington's Human Interface Technology Laboratory in Seattle, Washington USA. The VRD scans light directly onto the viewer's retina. The viewer perceives a wide field of view image. Because the VRD scans light directly on the retina, the VRD is not a screen based technology.
The VRD was invented at the University of Washington in the Human Interface Technology Lab (HIT) in 1991. The development began in November 1993. The aim was to produce a full color, wide field-of-view, high resolution, high brightness, low cost virtual display. Microvision Inc. has the exclusive license to commercialize the VRD technology. This technology has many potential applications, from head-mounted displays (HMDs) for military/aerospace applications to medical society.
The VRD projects a modulated beam of light (from an electronic source) directly onto the retina of the eye producing a rasterized image. The viewer has the illusion of seeing the source image as if he/she stands two feet away in front of a 14-inch monitor. In reality, the image is on the retina of its eye and not on a screen. The quality of the image he/she sees is excellent with stereo view, full color, wide field of view, no flickering characteristics.
Our window into the digital universe has long been a glowing screen perched on a desk. It's called a computer monitor, and as you stare at it, light is focused into a dime-sized image on the retina at the back of your eyeball. The retina converts the light into signals that percolate into your brain via the optic nerve.
Here's a better way to connect with that universe: eliminate that bulky, power-hungry monitor altogether by painting the images themselves directly onto your retina. To do so, use tiny semiconductor lasers or special light-emitting diodes, one each for the three primary colors-red, green, and blue-and scan their light onto the retina, mixing the colors to produce the entire palette of human vision. Short of tapping into the optic nerve, there is no more efficient way to get an image into your brain. And they call it the Virtual Retinal Display, or generally a retinal scanning imaging system.
The Virtual Retinal Display presents video information by scanning modulated light in a raster pattern directly onto the viewer's retina. As the light scans the eye, it is intensity modulated. On a basic level, as shown in the following figure, the VRD consists of a light source, a modulator, vertical and horizontal scanners, and imaging optics (to focus the light beam and optically condition the scan). 

The resultant imaged formed on the retina is perceived as a wide field of view image originating from some viewing distance in space. The following figure illustrates the light raster on the retina and the resultant image perceived in space.

In general, a scanner (with magnifying optics) scans a beam of collimated light through an angle. Each individual collimated beam is focused to a point on the retina. As the angle of the scan changes over time, the location of the corresponding focused spot moves across the retina. The collection of intensity modulated spots forms the raster image as shown above

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